<nav class="navbar navbar-inverse navbar-fixed-top" role="navigation">
      <div class="container">
        <div class="navbar-header">
          <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-expanded="false" aria-controls="navbar">
            <span class="sr-only">切换导航栏</span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
          </button>
          
          <a class="navbar-brand" href="#"><img src="img/logo.png"  style="margin-top: -5px;" class="img-circle img-responsive center-block"></a>
          <a class="navbar-brand" href="#">微博</a>
        </div>
        <div id="navbar" class="collapse navbar-collapse">
          <ul class="nav navbar-nav">
            <li class="active"><a href="#">首页</a></li>
            <li><a href="#about">视频</a></li>
            <li><a href="#contact">发现</a></li>
          </ul>
           <form class="navbar-form navbar-right" role="form">
            <div class="form-group">
              <input type="text" placeholder="请输入账号" class="form-control">
            </div>
            <div class="form-group">
              <input type="password" placeholder="请输入密码" class="form-control">
            </div>
            <button type="submit" class="btn btn-success">登录</button>
          </form>
        </div><!--/.nav-collapse -->
      </div>
    </nav>